With rapidly rotating bodies, for example spinning rotors, an imbalance occurs when the mass of the body is distributed in such a way that the center of gravity lies outside of the axis of rotation, or if the axis of rotation and the axis of inertia are not coincident. The imbalance results in undesired reaction forces during the rotation of the body causing uneven running or vibrations, which in particular increase considerably as rotational speed increases and/or in certain frequency ranges. Undesired results can occur, for example, loud noises, malfunctions, wear or even destruction of the rotor, which require maintenance or the replacement of such unbalanced components. Expense and downtime are created because of maintenance and replacement work, and the efficiency and/or the productivity, of the machine is negatively affected.
To prevent such disadvantages, dynamic balancing is customarily performed as a portion of the production process of such rapidly rotating bodies. In some cases, the mass equalization of the body can be accomplished by the installation of weights or in most cases by the removal of material from the body.
Presently the operating speed of spinning rotors in open-end spinning machines already is greater than 100,000 rpm. With such high numbers of revolution, the bearings and drive mechanisms of the spinning rotors are exposed to enormous stresses, together with the above described disadvantages, even in cases of small imbalances. It is therefore well known that it is imperative to not only produce spinning rotors with the highest precision in shape, but also to balance them carefully. In accordance with the known prior art, the balancing the spinning rotors by the removal of material is accomplished by grinding its exterior circumference. Grinding is customarily performed on the rotor cup at the end edge of the collar and at the exterior circumference at the location of its greatest circumference. Balancing of this type is known, for example, from European Patent Document EP 0 099 490 B1, as well as German Patent Publication DE 43 12 365 A1.
Balancing, already described as the prior art in European Patent Document EP 0 099 490 B1, is performed by grinding the exterior circumference of the spinning rotor. Although the removal of material as described in this reference has a considerable effect, the relatively thin wall of open-end spinning rotors, particularly in those rotors formed by a non-cutting formation process, is weakened at a critical point. In European Patent Document EP 0 099 490 B1 it is already expressly pointed out that such weakening must be absolutely avoided in view of the high number of rotor revolutions which is customary today. A balancing method is therefore disclosed in this reference wherein a first production step accomplishes mass equalization by initially punching a hole through the bottom of the rotor cup in the course of the compression process, and thereafter the hole may be enlarged to a degree sufficient for mass equalization. Such method, however, is expensive, time-consuming and, in particular, is limited to spinning rotors made by plastic deformation, for example from sheet metal.
German Patent Publication DE 43 12 365 A1 describes a rotor balancing method by grinding of the rotor collar. However, the considerable outlay required in the course of such balancing is disadvantageous.
German Patent Publication DE 43 39 064 A1 discloses a balancing method wherein balancing is performed by means of a pulsating laser beam. The pulse frequency of the laser beam is synchronized with the rotating speed of the rotor within an imbalance measuring device during the balancing process, such that the laser removes material when the unbalanced portion of the rotor turns past the impact point of the laser on the surface of the rotor. However, this method does not operate with sufficient precision for the exact balancing necessary to meet the desired quality requirements to balance the body for operation at high numbers of revolution. The exact guidance of the rotor during the rotating movement in the course of the balancing process is an absolute prerequisite for precise balancing by means of such a method, but is either too inaccurate or extraordinarily elaborate and therefore too expensive.